1. Field of the Invention
The present invention generally relates to a plasma deposition apparatus used in a semiconductor manufacturing process; particularly to a shower plate provided in the apparatus.
2. Description of the Related Art
A conventional plasma CVD apparatus possesses a first and a second electrode disposed parallel to each other inside a vacuum chamber; the first electrode has a hollow structure for introducing source gases into the vacuum chamber and has a shower plate removably attached in its bottom face; in the shower plate, many gas outlet holes or apertures are formed.
A conventional shower plate is disk-shaped and has many gas outlet apertures (e.g., 3,000 to 5,000) of a given diameter being formed in an arrangement adapted to pass completely through to the reverse face of the shower plate from its front face. Additionally, in the conventional shower plate, apertures are symmetrically distributed along its axis typically in a honeycomb-shaped surface pattern.
However, conventional plasma CVD apparatuses have a problem in that it is difficult to form a thin film having desired properties stably with excellent controllability or reproducibility. That is, the operable ranges to produce desired films are narrow.